1. Field of the Invention
This invention relates to an apparatus for continuous gelatin and noodling of a gelatin dispersion, and more particularly to an improved apparatus for achieving efficient water-washing of a photographic gelatin dispersion by forming noodles of relatively small diameter from said dispersion so as to increase the surface area to volume ratio of a gelled dispersion.
The term "gelatin dispersion" as used herein includes a photosensitive silver halide emulsion prepared by mixing solutions of potassium bromide and silver nitride in the presence of gelatin made of cattle hide or bone which is optionally mixed with an additive, and a dispersion of color-forming coupler dissolved in a mixture of an organic solvent and a water-soluble auxiliary solvent or a solvent of low water solubility, the resulting solution then being emulsified in a water soluble gelatin solution. Prior to coating on a support, such "gelatin dispersion" is freed of any water soluble by-product or auxiliary solvent that is deleterious to the quality of a photographic product. The "gelatin dispersion" is hereunder sometimes referred to as a dispersion.
2. Description of the Prior Art
An efficient method of removing water soluble byproducts and auxiliary solvent from a gelatin dispersion by making noodles of the dispersion is described in U.S. Pat. No. 3,396,027 wherein dispersions directly from the mixing operation and a colloid mill or homogenizer used in their preparation are passed continuously through the porous diaphragm or head of an extruder made of a heat insulating material such as glass or polystyrene into cold water in a washing tank to prepare gelled noodles of the dispersion as well as to free the noodles of the aforementioned impurities that are dissolved in the cold water.
The method combines the gelatin and noodling of the dispersion into a continuous flow process, thus not only obviating a large-capacity cooling unit for gelling the dispersion and temporarily storing the gelled dispersion but also achieving significant reduction in the pressure necessary for extruding the gelled dispersion into noodles. However, since the method employs an extruder made of a heat insulating material, the rate of cooling the dispersion upstream of the porous diaphragm is so low that to provide noodles stable against the subsequent washing with cold water accompanied by some degree of agitating effect, either the temperature at which the dispersion was prepared or the temperature of the cold water must be lowered, or the quantity of the dispersion to be extruded through the porous diaphragm into the cold water must be reduced. But to lower the temperature of the cold water means an increased load on the apparatus for producing cold water, and if the temperature of the dispersion to be supplied is decreased, the dispersion becomes highly viscous and requires higher pressure for extrusion. An attempt to throttle the dispersion to be extruded by reducing the diameter of each orifice in the porous diaphragm results only in noodles which easily break down to cause some of them to be lost as "fines".
Therefore, various studies have been made on the relationship between the construction or material of the extruder, particularly its porous diaphragm, and the stability of the noodles, and the apparatus of this invention which will be described hereunder has resulted.